Desulfurization of hydrocarbon oils



United States Patent Office 3,063,936 Patented Nov. 13, 1962DESULFURIZATEON F HYDROCARBON (EELS Thomas James Perrett Pearce andWilliam Stannage,

Norton-on-Tees, England, assignors to Imperial Chemical IndustriesLimited, London, England, a corporation of Great Britain No Drawing.Filed Aug. 20, 1959, Ser. No. 834,946 Claims priority, application GreatBritain Aug. 22, 1958 12 Claims. (Cl. 208-211) This invention relates todesulfurization of hydrocarbon oils.

Hydrocarbon oils, such as for example those obtained by fractionaldistillation of petroleum, often are contaminated with sulfur containingimpurities. For many purposes it is desirable that such impuritiesshould be removed. For example desulfurization of the hydro carbonfeedstock is a necessary step in the manufacture of methanol from amixture of carbon monoxide and hydrogen produced by steam reforming of astraight-run naphtha. In this process it is essential that the naphthashould be substantially free from sulfur, because if the sulfur contentof the naphtha is greater than about 5 p.p.m. the catalyst used in thesteam reforming process deteriorates rapidly under normal commercialconditions.

Several desulfurization processes are at present known which make a bigdecrease in the sulfur content of hydrocarbon oils. For example thesulfur content of a straightrun naphtha may be decreased from 200-1000p.p.m. to 20100 p.p.m. by treatment with sulfuric acid. The degree ofdesulfurization depends on the amount of acid used and on thethoroughness with which the acid and the hydrocarbon are mixed.Alternatively partial desulfurization may be achieved byhydrodesulfurization. For example we have found that the sulfur contentof a straight-run naphtha of boiling range up to 165 C. may be decreasedfrom 357 p.p.m. to -26 p.p.m. by passing the vapor mixed with anequimolecular volume of hydrogen at 50 atmospheres pressure over acatalyst comprising cobalt molybdate on alumina at 380 C. A similardegree of desulfurization may be achieved by passing the vapor, with orwithout hydrogen, over a contact material comprising zinc oxide,manganese oxide or iron oxide at 350 C. to 450 C.

No known desulfurization process is capable of achieving in one stage adecrease to less than 5 p.p.m. of the sulfur content of straight-runnaphthas commonly available. However, we have found that the problem ofeconomically achieving this degree of desulfurization is solved by usinga process comprising a novel combination of desulfurization stages ashereinafter specified.

According to the present invention, therefore, there is provided aprocess for desulfurization of a hydrocarbon oil which is substantiallyfree from ethylenically or acetylenically unsaturated compounds, whichprocess comprises three stages, of which the first stage comprisestreating the hydrocarbon oil with sulfuric acid under conditions ashereinafter specified, and/ or vaporizing it and then passing the vaporthus produced over a contact material comprising zinc oxide, manganeseoxide or iron oxide (preferably zinc oxide) at a temperature between 350C. and 450 C. and at a pressure between 1 and 50 atmospheres, the secondstage comprises passing the vaporized hydrocarbon, together withhydrogen, at a temperature between 350 C. and 450 C. and at a pressurebetween 1 and 50 atmospheres, over a hydrodesulfurization catalyst, andthe third stage comprises contacting the product from the second stagewith a hydrogen sullide absorbing material.

As stated above the first stage of the process comprises one or both oftwo specified desulfurization steps. However, it is preferred that thefirst stage include both of these stepsi.e. treating the hydrocarbon oilwith sulfuric acid, then vaporizing it and passing the vapor thusproduced over a contact material comprising zinc oxide, manganese oxideor iron oxide (preferably zinc oxide) under conditions as hereinbeforespecified.

The sulfuric acid treatment may conveniently be effected at or belowroom temperature. The temperature of the oil and acid mixture should notbe allowed to rise above about 40 C. A convenient concentration ofsulfuric acid is 90 to 98% by weight.

The oil and acid mixture remaining after the sulfuric acid treatmentstage may conveniently be separated electrostatically.

After electrostatic separation from the acid, the hydrocarbon oil ispreferably washed with an aqueous alkali, for example sodium hydroxide,to remove any remaining sulfuric acid, electrostatically separated fromthe alkali, and finally washed with water.

The separated acid may be recycled to the vessel in which thehydrocarbon oil and acid are mixed.

In the second stage of the process the temperature is preferably withinthe range 380 C. to 400 C., and the pressure is preferably between 4 and20 atmospheres.

Particularly suitable hydrodesulfurization catalysts are palladium,platinum or cobalt molybdate, supported on alumina. So-called cobaltmolybdate catalysts are well known and comprise the oxides of cobalt andmolybdenum either as such or in combined form.

Any suitable material which is capable of absorbing hydrogen sulfide maybe used in the third stage of the process. However, the absorbingmaterial preferably comprises Zinc oxide, manganese oxide or iron oxide(zinc oxide being preferred). These substances have the advantage thatthey will eifectively absorb hydrogen sulfide from the hot hydrocarbonvapor, which therefore does not have to be cooled first.

The treatment with a contact material comprising zinc oxide, manganeseoxide or iron oxide which may comprise at least part of the first stageof the process, and the second and third stages of the process mayconveniently be effected in one operation by passing the hydrocarbonvapor, mixed with hydrogen, through a sandwich consisting of a bed ofhydrodesulfurization catalyst between two beds each of which compriseszinc oxide, manganese oxide or iron oxide.

The process of the present invention is particularly suitable fordesulfurization of a straight-run naphtha, by which is meant a mixtureof paraffinic, naphthenic and aromatic hydrocarbons obtained byfractional distillation of petroleum and having a boiling range of about10 C.

to about 200 C. The process is not suitable for desulfurization ofhydrocarbons containing substantial amounts of ethylenically oracetylenically unsaturated compounds, such as for example hydrocarbonsobtained as a result of a thermal cracking process.

When a straight-run naphtha is desulfurized according to the presentinvention, in the second stage of the process the naphtha is mixed withhydrogen preferably in a 1:1 molar ratio.

We have found that in order to reduce the sulfur content of astraight-run naphtha from 5002000 p.p.m. to 25 p.p.m. or less, which ishighly desirable if the naphtha is to be used in a steam reformingprocess for the production of methanol synthesis gas, it is importantthat most of the sulfur should be removed before thehydrodesulfurization stage. In the process of .the present inventionsulfur is removed in the first stage of the process. In the second stepwhich it is preferred to include in the first stage of the process thebed of zinc oxide or its equivalent removes substantially the entireremaining tans, sulfides and disulfides. It is believed that theseimpurities are either absorbed as such or hydrogenated to hydrogensulfide which is then absorbed. Thus the amount ofsulfur remaining isvery small; .The hydrode- 'sulfurization catalyst catalyses thehydrogenation of organic sulfur compounds, such as for examplethiophenes and thiophanes, to hydrogen sulfide, which is absorbed by thefinal bed of zincoxide or its equivalent. The ratio of hydrogen tohydrogen sulfide in contact with the hydrodesulfurization catalyst isvery high. Consequently it is impossible for any detectable amount oforganic sulfur compounds to exist in equilibrium with hydrogen and thehydrogen sulfide formed in the hydrodesulfurization reaction, and a veryhigh degree of sulfur removed can be obtained.

The mixture of hot desulfurized naphtha vapor and hydrogen, which isproduced by the preferred process of the present invention, may be mixedwith steam and used as the feed in a steam reforming process forproduction of methanol synthesis gas. This of course is only one use ofthe invention, which finds a wide application to industrial processeswhere hydrocarbon oils need to be desulfurized to a high degree.

The following examples are illustrative of the process of the presentinvention.

Example 1 I A Venezuelan straight-run naphtha of specific gravity 0.746and boiling range 103 C. to 164 C. containing 250 p.p.m. of sulfur waspassed through a bed of zinc oxide at 400 C. at a liquid hourly spacevelocity of 0.75. The sulfur content of the product was 56 p.p.m. Thispartially purified material, mixed with an equimolar volume of hydrogen,was then passed through a catalyst comprising 0.3% platinum on aluminaat 385 C., and then through a bed of zinc oxide in the form of 45 inchpills at 385 C. to 390 C. The liquid hourly space velocities throughthese beds were respectively 1.1 and 0.75. The sulfur content of theproduct was less than 1 p.p.m.

Example 2 A straight-run naphtha of specific gravity 0.72 approxi-Temperatur 1 C 380 Pressur 7 lbs./in. 45 Liquid hourly space velocityover cobalt molybdate catalys 0.9 Liquid hourly space velocity over zincoxide pills 1.2

The sulfur content of the product after the seven days run of theexperiment was 1-3 p.p.m.

- 'Example 3 A straight-run Kuwait naphtha of specific gravity 0.725 andboiling range 55C. to 166C. containing 250 p.p.m. of sulfur was treatedwith 2% by Weight of 96% sulfuric acid in a paddle type mixer, washedwith 10% caustic soda, and finally washed with Water. This treatmentdecreased the sulfur content to 20 p.p.m.

The naphtha was then vaporized, mixed with an equimolecular volume ofhydrogen and preheated to 400 C. under atotal pressure of 16atmospheres. The mixture of naphtha and hydrogen was then passedsuccessively througha bed of zinc oxide pi]ls, a bed of cobalt molybdatepellets, and finally a second bed of zinc oxide pills. The liquid hourlyspace velocities through these beds were respectively 2.4, 1.0,and 2.4.The total sulfur content of the naphtha after this treatment was 3-5p.p.m.

We claim:

1. A process for desulfurization of straight-run petroleum naphtha whichis substantially free from ethylenically and acetylenicaly unsaturatedcompounds com- 5 prising (1) contacting said oil with sulfuric acid,

(2) separating the acid from the oil,

(3) vaporizing said oil,

(4) passing the vapors of said oil in contact With a material selectedfrom the group consisting of zinc oxide, manganese oxide and iron oxideat a temperature between 350 C. and 450 C. and a pressure of :between 1and 50 atmospheres,

(5) contacting the resulting gas together with hydrogen with ahydroclesulfurization catalyst at a temperature of 350-450 C. and apressure between 1 and 50 atmospheres and then (6) contacting theresulting product, while vaporized, with a material selected from thegroup consisting of zinc oxide, manganese oxide and iron oxide to removehydrogen sulfide,

whereby the sulfur content of the hydrocarbon material is reduced to atmost 5 parts per million.

2. A process for desulfurization of a straight run petroleum naphthawhich is substantially free from ethylenically and acetylenicallyunsaturated compounds comprising treating said oil with sulfuric acid,separating the oil from the acid, (3) vaporizing the oil separated fromsaid acid, (4) contacting the vapors together with hydrogen with ahydrodesulfurization catalyst at a temperature of between 350 C. and 450C. and a pressure of between 1 and 50 atmospheres and then (5 contactingthe resulting product, while vaporized, with a material selected fromthe group consisting of zinc oxide, manganese oxide and iron oxide toremove hydrogen sulfide, whereby the sulfur content of said oil isreduced to at most 5 parts per million.

3. A process according to claim 2 in which the sulphuric acid is of 90%to 98% concentration by weight.

4. A process according to claim 2 in which the naphtha and acid mixtureremaining after the sulphuric acid treatment stage is separatedelectrostaticall y.

5. A process according to claim 4 in which the separated naphtha isWashed with aqueous alkali, electrostatically separated from the saidalkali, and then washed with water. K V V 6. A process according toclaim 2 in which the hydrodesulfurization catalyst is an aluminasupported catalyst selected from the group consisting of palladium,platinum and cobalt molyb date.

7. A process according to claim 1 in which the naphtha is mixed withhydrogen in a 1:1 molar ratio while in contact with ahydrodesulfurization catalyst. 8. A process according to claim 2 inwhich sulfuric acid separated from the naphtha after treatment thereofis recycled and combined with crude hydrocarbon oil for acid treatmentof the oil.

9. A process according to claim 2 in which the naphtha is contacted withsaid hydrodesulfurization catalyst at a temperature Within the rangeof380 C. to 400 C.

10. A process according to claim 2 in which the naphtha is contactedwith said hydrodesulfurization catalyst at a pressure between 4 and 20atmospheres.

11. A process for desulfurization of a straight run petroleum naphthawhich is substantially free from ethylenically and acetylenicallyunsaturated compounds comprising (1) vaporizing said oil,

(2) passing the vapors of said naphtha in contact with l a materialselected from the group consisting of zinc oxide, manganese oxideandiron oxide at a tempera- 5 ture between 350 C. and 450 C. and apressure of between 1 and 50 atmospheres,

(3) passing the vaporized hydrocarbon and hydrogen over ahydrodesulfurization catalyst at a temperature between 350 C. and 450 C.and a pressure of between 1 and 50 atmospheres and (4) then contactingthe resulting product, while vaporized, with a material selected fromthe group consisting of zinc oxide, manganese oxide and iron oxide toremove hydrogen sulfide,

whereby the sulfur content of the hydrocarbon material is reduced to atmost 5 parts per million.

12. A process for desulfurization as set forth in claim 11 in which theoil is passed through a sandwich consisting of a bed ofhydrodesulfurization catalyst between two beds each of which comprisesmaterial selected from the group consisting of zinc oxide, manganeseoxide and iron oxide.

References Cited in the file of this patent UNITED STATES PATENTS2,300,877 Drennan Nov. 3, 1942 2,636,843 Arnold et a1 Apr. 28, 19532,769,760 Annable et a1. Nov. 6, 1956 2,769,763 Annable et al Nov. 6,1956 2,845,382 Leum et a1. July 29, 1958 2,897,142 Jacobs et a1. July28, 1959 2,944,015 Rausch et al. July 5, 1960 2,959,538 Weikart et a1Nov. 8, 1960 2,973,315 Watson Feb. 28, 1961

1. A PROCESS FOR DESULFURIZATION OF STRAIGHT-RUN PETROLEUM NAPHTHA WHICHIS SUBSTANTIALLY FREE FROM ETHYLENICALLY AND ACETYLENICALY UNSARURATEDCOMPOUNDS COMPRISING (1) CONTACTING SAID OIL WITH SULFURIC ACID, (2)SEPARATING THE ACID FROM THE OIL, (3) VAPORIZING SAID OIL, (4) PASSINGTHE VAPORS OF SAID OIL IN CONTACT WITH A MATERIAL SELECTED FROM THEGROUP CONSISTING OF ZINC OXIDE, MANGANESE OXIDE AND IRON OXIDE AT ATEMPERATURE BETWEEN 350*C. AND 450*C. AND A PRESSURE OF BETWEEN 1 AND 50ATMOSPHERES, (5) CONTACTING THE RESULTING GAS TOGETHER WITH HYDROGENWITH A HYDRODESULFURIZATION CATALYST AT A TEMPERATURE OF 350-450*C. ANDA PRESSURE BETWEEN 1 AND 50 ATMOSPHERES AND THEN (6) CONTACTING THERESULTING PRODUCT, WHILE VAPORIZED, WITH A MATERIAL SELECTED FROM THEGROUP CONSISTING OF ZINC OXIDE, MANGANESE OXIDE AND IRON OXIDE TO REMOVEHYDROGEN SULFIDE, WHEREBY THE SULFUR CONTENT OF THE HYDROCARBON MATERIALIS REDUCED TO AT MOST 5 PARTS PER MILLION.